You'll be redirected to Roblox's gift cards page. Tap on Redeem, located at the very top of the page. Enter the empty Code field with your Roblox gift card's code, then tap Redeem to finish.

How to Redeem Promo Codes in Roblox Redeeming promo codes in Roblox is very straightforward, though admittedly the site placed it in a rather awkward place.